The Sudden Infant Death Syndrome (SIDS) remains a leading cause of infant deaths in spite of successful public health interventions designed to reduce SIDS risks. In recent years there has been little further decline in SIDS deaths. Progress depends on a better understanding of pathophysiology and risk factors. We propose to study physiologic mechanisms potentially involved in the etiology of SIDS in particular those producing stresses resulting in death. First we will investigate the potential role of upper airway obstruction during sleep in SIDS. The diagnostic potential of transthoracic impedance (TTI) monitoring will be studied in mice, rabbits and human infants with apneic spells at various developmental stages. These results will be applied to analysis of fatal event TTI recordings of infants including SIDS infants. The purpose of these studies is to determine if specific breathing patterns are characteristic of SIDS and if airway obstruction, cardiovascular shock or certain irregularities in autoresuscitation (AR) mechanisms are present. Also, studies of upper airway sensory motor mechanism that may facilitate AR will be performed in the animal models. These studies may suggest developmental or other abnormalities in cardiorespiratory brainstem centers in SIDS victims. Additionally, in healthy infants we will determine if the prone sleep position predisposes to obstructive sleep apnea. Finally, we will study Medical Examiner's records (St. Louis, MO.) of infants dying suddenly and unexpectedly to determine if post mortem body temperature indicates involvement of overheating or disorders of thermoregulation in SIDS. [unreadable] [unreadable]